This invention is directed to a control system for a complete manufacturing system for small-order-quantity, complex goods. The control system of this invention has the capability of rapid information processing and display, minimization of manufacturing cycle time, efficient allocation of resources, and minimized excess costs.
Although the invention has general application to a wide range of manufacturing systems, it will be illustratively described with specific reference to the manufacture of gearboxes.
In the manufacture of small-order-quantity, complex goods such as gearboxes, the work effort is a sequence of machining and assembly operations. The proper control of these operations is as important to the efficient transformation of the raw steel into the finished gearbox as each machining operation itself. Just as an improvement in the cutting method of the gears can produce faster, lower-cost production, an improvement in the control of manufacturing operations can produce a similar reduction in total cost and the elapsed time of production.
For example, in U.S. Pat. No. 3,703,725, the method of control uses a computer to balance work flow rates in a manufacturing process. In U.S. Pat. No. 3,845,286, a control system sequences semi-conductor wafers through a number of work stations. In U.S. Pat. No. 4,027,246, a central computer controls the transfer and processing of semi-conductor wafers. Although these inventions teach a means for manufacturing control, and an improvement in efficiency, they do not teach a means to maximize manufacturing efficiency and thereby minimize manufacturing costs.
In the manufacture of complex, small-order-quantity goods, the costs of idle waiting time, penalties due to late delivery, unjustified expediting costs, and excessive inventories must be minimized.
One system that has addressed this problem is the critical path method (CPM), in which a network of activities is created that shows the sequence of operations and the interdependencies of the particular manufacturing process. A variation of this basic method is PERT (Project Evaluation and Review Technique) which uses multiple estimates to provide a probabilistic output. These systems are frequently computerized and searched to find the critical item; i.e., the item that is, in effect, the latest, and which determines the final completion date.
The major problem with these systems is that critical items must be searched serially; each requiring a computer run, at a considerable expense in large projects. Further, for every change in the availability date of any item, the impact on the final completion date can only be assessed by another computer run. In general, these systems do not provide an easy and timely visability into the critical items and their degree of impact. Also, these systems do not offer a means to balance resources in order to minimize the costs of the project.